Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, FIG. 1 depicts a conventional magnetic tunneling junction (MTJ) 10 as it may be used in a conventional STT-MRAM. The conventional MTJ 10 typically resides on a substrate 12. A bottom contact 14 and a top contact 22 may be used to drive current through the MTJ 10. The MTJ uses seed layer(s) and may include capping layers and an antiferromagnetic (AFM) layer (not shown). The conventional MTJ 10 includes a pinned layer 16, a tunneling barrier layer 18, and a free layer 20. Contacts 14 and 22 are used in driving the current in a current-perpendicular-to-plane (CPP) direction, or along the z-axis as shown in FIG. 1. Typically, the pinned layer 16 is closest to the substrate 12 of the layers 16, 18 and 20.
The pinned layer 16 and the free layer 20 are magnetic. The magnetization 17 of the pinned layer 16 is fixed, or pinned, in a particular direction. Although depicted as a simple (single) layer, the pinned layer 16 may include multiple layers. For example, the pinned layer 16 may be a synthetic antiferromagnetic (SAF) layer including magnetic layers antiferromagnetically coupled together through thin conductive layers, including, for instance, Ru. In such a SAF, multiple magnetic layers interleaved with thin layers of Ru may be used. In another embodiment, the coupling across the Ru layers can be ferromagnetic.
The free layer 20 has a changeable magnetization 21. Although depicted as a simple layer, the free layer 20 may also include multiple layers. For example, the free layer 20 may be a synthetic layer including magnetic layers antiferromagnetically or ferromagnetically coupled through thin conductive layers, including, for instance Ru. Although shown as perpendicular-to-plane, the magnetization 21 of the free layer 20 may alternatively be in plane. Thus, the pinned layer 16 and free layer 20 may have their magnetizations 17 and 21, respectively oriented in plane with the layers.
To switch the magnetization 21 of the free layer 20, a current is driven perpendicular to plane (in the z-direction). When a sufficient current is driven from the top contact 22 to the bottom contact 14, the magnetization 21 of the free layer 20 may switch to be parallel to the magnetization 17 of the pinned layer 16. When a sufficient current is driven from the bottom contact 11 to the top contact 22, the magnetization 21 of the free layer may switch to be antiparallel to that of the pinned layer 16. The differences in magnetic configurations correspond to different magneto-resistances and thus different logical states (e.g. a logical “0” and a logical “1”) of the MTJ 10.
Because of their potential for use in a variety of applications, research in magnetic memories is ongoing. For example, mechanisms for improving the performance of STT-RAMs are desired. More specifically, MTJs providing lower switching current and higher read-out signals are desirable. Accordingly, what is needed is a method and system that may improve the performance of spin transfer torque based memories. Among other things, it would be desirable to have a method and system of producing an STT-RAM device that has improved tunneling magneto-resistance (TMR), perpendicular magnetic anisotropy (PMA), and spin wave damping properties through the reduction of boron (B) content in the MTJ layers, such as the free layer and/or the pinned layer. The method and system described herein address such a need.